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The pressure chamber is the most used tool for plant water status monitoring. However, species/cultivar and seasonal effects on protocols for reliable water potential determination have not been properly tested. In four grapevine cultivars and two times of the season (early season, Es; late season, Ls, under moderate drought), we assessed the maximum sample storage time before leaf water potential (Ψleaf) measurements and the minimum equilibration time for stem water potential (Ψstem) determination, taking 24 h leaf cover as control. In 'Pinot gris', Ψleaf already decreased after 1 h leaf storage in both campaigns, dropping by 0.4/0.5 MPa after 3 h, while in 'Refosk', it decreased by 0.1 MPa after 1 and 2 h in Es and Ls, respectively. In 'Merlot' and 'Merlot Kanthus', even 3 h storage did not affect Ψleaf. In Es, the minimum Ψstem equilibration was 1 h for 'Refošk' and 10 min for 'Pinot gris' and 'Merlot'. In Ls, 'Merlot Kanthus' required more than 2 h equilibration, while 1 h to 10 min was sufficient for the other cultivars. The observed cultivar and seasonal differences indicate that the proposed tests should be routinely performed prior to experiments to define ad hoc procedures for water status determination. [ABSTRACT FROM AUTHOR]

• Deficit irrigation (35% ET 0) does not reduce stem water potential (Ψ stem) below water stress levels in Merlot Khorus. • Stomatal conductance (g s) and net photosynthesis (A N) are negatively affected by deficit irrigation in Merlot Khorus. • The basal crop coefficient (K cb) of Merlot Khorus in northeast Italy is far different from what suggested by standard methodologies. • Merlot Khorus is suitable for deficit irrigation management. Fungus–resistant varieties are gathering attention all over viticultural areas owing to their contribution to sustainable management. Sustainable viticulture implies lower inputs in terms of pesticides and water. However, investigations on the physiological behavior of fungus–resistant varieties under drought stress have been seldom conducted so far. Under climate change conditions, evaluating precise water use is particularly important to set up proper irrigation. In this study, a two-year experiment was imposed to characterize the physiological behavior of the fungus–resistant variety Merlot Khorus under two contrasting water regimes (full irrigation, WW; water deficit, WD). Berry weight and grape quality in the two treatments was also compared to evaluate the feasibility of adopting deficit irrigation strategies in the region. The study was conducted in the Friuli Venezia Giulia region (Italy). The measured values of stem water potential (Ψ stem) did not highlight any severe water stress (> -1.15 MPa) in WD. However, g s and A N decreased to values typical of drought–stressed vines. Concurrently, the experiment assessed that the calculated Kcb of Merlot Khorus in northeast Italy is far different from what has been suggested by standard methodologies and the literature. The grapes under deficit irrigation showed reduced berry weight, while basic maturation parameters and anthocyanins were improved. Overall, the study indicated that Merlot Khorus appears to be a genotype suitable for dry farming or deficit irrigation management in northeastern Italy. Therefore, the results may help winegrowers to improve irrigation strategies. [ABSTRACT FROM AUTHOR]

Studying changes in partitioning of dry matter and nonstructural carbohydrates (NSC) content in both aboveground and underground perennial tissues in drought-affected grapevines could provide insights into plant response and carbon allocation strategies during stress periods. The analysis of soluble NSC and starch content in leaf petioles, due to their role in hydraulic segmentation, should also be considered. In the present research, these aspects have been investigated in Merlot grapevines grown in pots and subjected to progressive and increasing soil dehydration, and in well-irrigated vines. Drought conditions caused drastic reduction of shoot elongation and total plant leaf area development in favor of a greater biomass allocation and partitioning towards roots, where most of the NSC reserves were also conserved. Dry matter content of the perennial organs increased in stressed vines due to growth reduction, allocation of carbon reserves and possible anatomical modifications. Vines subjected to drought showed a higher NSC content in petioles, supporting the hypothesis that they are involved as compatible solutes in osmotic adjustments. [ABSTRACT FROM AUTHOR]